UV-260
– USER MANUAL
8
Positive discharge is homogeneous, as the majority of charges are concentrated close to the
electrode. Negative discharge at the same voltage takes a larger area, but because the energy is
spread over the wider area, it seems to be weaker and it may be difficult to locate.
In practice, controlled corona discharges, are used for example in industry to remove dust in
the gases, air, or to remove unwanted electric charges (even in household air ionizers). Charges
are generated on certain surfaces and this phenomena may be observed in many everyday items
e.g. a laser printer or photocopier.
3.3.
Why corona discharge?
Unwanted corona discharge influence adversely the devices, where they occur, for example by
causing radio interference (often problems with the reception of radio signals near high voltage
power lines), or by causing a loss of energy (energy "escapes" to the air). The most adverse effect
of corona discharges, is the impact on the insulation elements, resulting in the need to disconnect
entire power transmission systems. Therefore, it is required to prevent corona discharges and
reduce them at their early stage, as the next stage results in creating an arc and permanent
damage.
Even the presence of small discharges in one place may cause adverse effects, because the
current flow and contamination generate corrosive substances, which deteriorate the condition of
insulators, enable the moisture access to the internal components and accelerate degradation.
Locating corona discharges is a useful cautionary measure, similarly to infra-red methods that help
to discover potential problems before they arise.
3.4.
Detection of corona discharge
UV-260 detects and locates corona discharges by detecting the UV signal generated during the
discharge, then they can be counted to assess the level of discharge. In practice, the number of
discharges in a certain time is represented graphically - by so called 'UV image'. Precise overlay of
UV image on the real image provides an accurate and most importantly, safe (performed from a
distance) method of locating places where equipment degradation started, without the need to turn
off power of the tested facility.
Fig. 3, 4. Corona discharge in laboratory conditions.
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